Hexokinase II acts through UCP3 to suppress mitochondrial reactive oxygen species production and maintain aerobic respiration

Abstract

UCP3 (uncoupling protein-3) mitigates mitochondrial ROS (reactive oxygen species) production, but the mechanisms are poorly understood. Previous studies have also examined UCP3 effects, including decreased ROS production, during metabolic states when fatty acid oxidation is high (e.g. a fasting state). However, the role of UCP3 when carbohydrate oxidation is high (e.g. fed state) has remained largely unexplored. In the present study, we show that mitochondrial-bound HK (hexokinase) II curtails oxidative stress and enhances aerobic metabolism of glucose in the fed state in a UCP3-dependent manner. Genetic knockout or inhibition of UCP3 significantly decreased mitochondrial-bound HKII. Furthermore, UCP3 was required for the HKII-mediated decrease in mitochondrial ROS emission. Intriguingly, the UCP3-mediated modulation of mitochondria-associated HKII was only observed in cells cultured under high-glucose conditions. UCP3 was required to maintain high rates of aerobic metabolism in high-glucose-treated cells and in muscle of fed mice. Deficiency in UCP3 resulted in a metabolic shift that favoured anaerobic glycolytic metabolism, increased glucose uptake and increased sensitivity to oxidative challenge. PET (positron emission tomography) of [18F]fluoro-deoxyglucose uptake confirmed these findings in UCP3-knockout and wild-type mice. Collectively, our findings link the anti-oxidative and metabolic functions of UCP3 through a surprising molecular connection with mitochondrial-bound HKII.

Hexokinase II integrates energy metabolism and cellular protection: Akting on mitochondria and TORCing to autophagy

“…77,80,82,83,[96][97][98] A series of studies have demonstrated that mitoHK-II has an ability to decrease ROS generation at mitochondria to prevent opening of the mPTP. 77,80,82,84,99 As mentioned earlier, mitoHK ensures tight coupling of glucose phosphorylation and mitochondrial ATP generation. This increases electron flow in the mitochondria and thus decreases mitochondrial membrane potential, which can reduce mitochondrial ROS emission.…”

“…This increases electron flow in the mitochondria and thus decreases mitochondrial membrane potential, which can reduce mitochondrial ROS emission. 77,99 It has also been demonstrated that mitoHK-II has a direct inhibitory effect on the mPTP. The mechanism for the protection is not known, largely because the molecular composition of mPTP is not fully identified.…”

“…136 A recent study using UCP3 KO mice showed that UCP3 enhanced mitoHK-II binding in skeletal muscle, participating in a UCP3-mediated decrease in ROS emission. 99 (4) Another intriguing regulatory mechanism of mitoHK-II was obtained from studies of p53, a key tumor suppressor. In addition to the established role of p53 in cell cycle arrest and apoptosis, recent evidence has demonstrated that p53 reduces glycolytic flux and increases oxidative phosphorylation, halting the Warburg effect.…”

Glutaredoxin-2 Is Required to Control Proton Leak through Uncoupling Protein-3

“…Prior to HPLC, serum was diluted 10-fold. Mitochondrial Isolation-Skeletal muscle and liver mitochondria were isolated as described previously (11,35). All buffers were supplemented with 10 mM pyruvate and 2 mM malate or 10 mM succinate and filtered prior to use.…”

“…Metabolite Analysis-TCA cycle intermediate and ATP levels were assessed by HPLC as described previously (11). Mitochondria were diluted to 0.5 mg/ml in 0.5% v/v perchloric acid solution, incubated on ice for 10 min, and the precipitate removed by centrifugation.…”